001    // Copyright 2007, 2008, 2009 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    //     http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry5.services;
016    
017    import org.apache.tapestry5.PropertyConduit;
018    
019    /**
020     * A source for {@link org.apache.tapestry5.PropertyConduit}s, which can be thought of as a compiled property path
021     * expression. PropertyConduits are the basis of the "prop:" binding factory, thus this service defines the expression
022     * format used by the {@link org.apache.tapestry5.internal.bindings.PropBindingFactory}.
023     */
024    public interface PropertyConduitSource
025    {
026        /**
027         * Returns a property conduit instance for the given expression. PropertyConduitSource caches the conduits it
028         * returns, so despite the name, this method does not always create a <em>new</em> conduit. The cache is cleared if
029         * a change to component classes is observed.
030         * <p/>
031         * Callers of this method should observe notifications from the {@link org.apache.tapestry5.services.InvalidationEventHub}
032         * for {@link org.apache.tapestry5.services.ComponentClasses} and discard any aquired conduits; failure to do so
033         * will create memory leaks whenever component classes change (the conduits will keep references to the old classes
034         * and classloaders).
035         *
036         * @param rootType   the type of the root object to which the expression is applied
037         * @param expression expression to be evaluated on instances of the root class
038         * @return RuntimeException if the expression is invalid (poorly formed, references non-existent properties, etc.)
039         */
040        PropertyConduit create(Class rootType, String expression);
041    }